1. Field of the Invention
This invention relates to defect inspection systems and, more particularly, to apparatus and methods for high speed processing of images of objects such as fruit. The invention further facilitates the location of defects in the objects and separating those objects with defects from other objects that have only a few or no defects.
2. Description of the Related Art
The United States packs over 170 million boxes of apples each year. Although some aspects of the packing process are now automated, much of it is still left to manual laborers. The automated equipment that is available is generally limited to conveyor systems and systems for measuring the color, size, and weight of apples.
A system manufactured by Agri-Tech Inc. of Woodstock, Va., automates certain aspects of the apple packing process. At a first point in the packing system, apples are floated into cleaning tanks. The apples are elevated out of the tank onto an inspection table. Workers along side the table inspect the apples and eliminate any unwanted defective apples (and other foreign materials). The apples are then fed on conveyors to cleaning, waxing, and drying equipment.
After being dried, the apples are sorted according to color, size, and shape, and then packaged according to the sort. While this sorting/packaging process may be done by workers, automated sorting systems are more desirable. One such system that is particularly effective for this sorting process is described in U.S. Pat. No. 5,339,963.
As described, a key step of the apple packing process is still done by hand: the inspection process. Along the apple conveyers in the early cleaning process, workers are positioned to visually inspect the passing apples and remove the apples with defects, i.e., apples with rot, apples that are injured, diseased, or seriously bruised, and other defective apples, as well as foreign materials. These undesirable objects, especially rotted and diseased apples, must be removed in the early stage (before coating) to prevent contamination of good fruit and to reduce cost in successive processing.
Working in a wet, humid, and dirty environment and inspecting large amounts of apples each day is a difficult and labor intensive job. With tons of apples passing in front of the eyes of workers, human fatigue is unavoidable; there are always misinspected apples passing through the lines.
Apples are graded in part according to the amount and extent of defects. In Washington State, for example, apples with defects are used for processing (e.g., to make into apple sauce or juice). These apples usually cost less than apples with no defects or only: a few defects. Apples that are not used for processing, i.e., fresh market apples, are also graded not only on the size of any defects, but also on the number of defects. Thus, it would be desirable to provide a system which integrates an apple inspection system that checks for defects in apples into the rest of the packing process.
A defect inspection and removal system would significantly innovate the fresh fruit packing process. It will liberate humans from traditional hand manipulation of agricultural products. By placing the defect inspection and removal system at the beginning of the packing line, it will eliminate bad fruit, contaminants, and foreign materials from getting into the rest of the packing process. This will reduce the costs of materials, energy, labor, and operations.
An automated defect inspection and removal system can work continuously for long hours and will never tire or suffer from fatigue. The system will not only improve the quality of fresh apples and the productivity of packing, but also improve the health of workers by freeing them from the wet and oppressive environment.
Twenty-five years ago a researcher identified three conditions for a suitable method of detecting bruises in apples. The method must be: (1) based on reliably identifiable bruise effects, (2) nondestructive, and (3) adaptable to high-speed sorting. T. L. Stiefvater, M. S. Thesis, Cornell University Agricultural Engineering Department, 1970.
In U.S. Pat. No. 3,867,041, Brown et al. proposed a nondestructive method for detecting bruises in fruit. That method relied solely on a comparison of the light reflected from a bruised portion of the fruit with the light reflected from an unbruised portion. A bruise was detected when the light reflected from the bruised portion was significantly lower than the amount of light reflected from the unbruised portion. However, Brown et al. failed to consider the spherical nature of fruit. Like the light reflectance at a portion of fruit with a bruise, the light reflectance at the outer perimeter of the fruit is also low. This is due to the substantially spherical nature of fruit. Thus, to effectively detect bruises in fruit, a method must consider the spherical nature of the object being processed. Brown et al. also failed to address the issue of having to distinguish bruises with low reflectance from background that also has low reflectance. Brown et al. offered no solution to either of these problems.
Conway et al. proposed a solution for considering the spherical nature of fruit in U.S. Pat. No. 4,246,098. That solution simply treated segments near fruit edges in the same manner as the background area--i.e., ignoring them. This can be a significant problem when a blemish is located in the ignored segments.
Another proposed system for detecting bruises in apples is described in U.S. Pat. No. 4,741,042. However, that system makes the erroneous fundamental assumption that all bruises, which are defined as surface blemishes, are circular in shape. (The bruise is determined by whether or not a segment is round.) Examination of a single truck load of apples shows that a great percentage of apples with defects have bruises that are not circular or otherwise uniform in shape. Further, the complete range of defects includes not only the minor circular surface bruises of the type described in U.S. Pat. No. 4,741,042 but also includes rots, injuries, diseases, and serious bruises, which may not be apparent from a simple viewing of the apple surface.